All four Democrats vying to fill the open Senate seat of the late Frank Lautenberg have plenty of liberal cred. We can expect them to vote the same way, nearly every time. But no matter. This is not a difficult choice, because our priorities in the Aug. 13 primary lie elsewhere.

What Congress really needs right now is not an orthodox liberal. It’s someone who would be willing to cross party lines, at least once in a while, for the sake of making a big deal. Someone who would join the “Gang of Eight” senators who hashed out a bipartisan agreement on immigration reform, as Sen. Robert Menendez (D-N.J.) did. Someone who works well with Republicans.

That someone, in our view, is Newark Mayor Cory Booker.

Thankfully, he has a strong lead over Reps. Frank Pallone (6th Dist.) and Rush Holt (12th Dist.), and Assembly Speaker Sheila Oliver (Essex). And whoever wins this primary will likely trounce the expected Republican nominee, Steve Lonegan, in the Oct. 16 special election.

Of Booker’s challengers, Pallone and Holt are the most alike, with similar voting records. Pallone helped write the Affordable Care Act, and fought hard for Hurricane Sandy relief and environmental causes like stopping ocean dumping. Holt, a physicist known for beating an IBM supercomputer on “Jeopardy!”, is a rare voice of scientific reason in the House, and a crusader on issues such as climate change and campaign finance reform.

Both are savvy, effective advocates. But they’re also more likely to obey their liberal base than take the political risk of reaching across the aisle. Each says, for instance, that he’d refuse to consider any cuts to Social Security or Medicare, without which there’s no way to solve our budget problem.

The math won’t work — and the politics, not even remotely. This position is to the left of President Obama, who has agreed to limit cost-of-living increases in Social Security as part of a deal.

Oliver took that pledge, too, although in the past she’s shown herself to be a shrewd deal maker. She worked constructively with Gov. Chris Christie and defied her own party to win much needed pension and health reforms. She’s right that we need more women in Congress. But while she’s been a good Speaker, she’s not nearly as well-versed on federal issues.

Which leaves Booker, our pick. He’s done a great job as mayor, with measurable progress on economic development, reducing violent crime, building affordable housing and parks. He deserves credit for removing the vestiges of Newark’s corrupt former mayor, Sharpe James, and making huge progress on ethics reform in this city. More importantly, Booker has stuck out his neck to support pension and health reform, and the education reform Newark needs. He’s a Democrat who has stood up to unions, his own constituency, to do the right thing.

We haven’t seen Pallone or Holt do that, at least not in the high-profile, central way Booker has. The Newark mayor also went out of his way to trumpet gay rights early on, which wasn’t easy given the skepticism from many African-Americans.

Booker has much greater potential to advance the national discussion, in part because he’s shown he’s willing to cross lines to make sensible deals, even if it offends core interest groups in the Democratic Party. And because he’s a lot more articulate and compelling, which is important in a senator.

He’ll use his powers of persuasion to advance resolutions, without being needlessly adversarial. The last thing we need is more partisan swordplay in Congress. And Cory Booker is part of the solution.